Aromatic copolyestercarbonates are well known as copolymers derived from carbonate precursors, dihydric phenols and aromatic dicarboxylic acid or acid derivatives. Among the properties characterizing these polymers is a relatively high distortion temperature under load (DTUL) as well as a relatively high impact strength as measured by a notched Izod test system. The impact failure mode, however, for both the 1/8 and 1/4 inch test pieces is brittle as opposed to ductile.
Aromatic polycarbonates are also well known polymers derived from carbonate precursors and dihydric phenols. Among the properties characterizing these polymer is a DTUL significantly lower than an aromatic copolyester carbonate and a high resistance to impact in thin section, i.e. a 1/8 inch test system which also involves a ductile failure mode. However as in the nature of most glassy polymers, aromatic polycarbonates have a critical thickness beyond which impact strength drops quite rapidly and the failure mode changes from ductile to brittle. The notched Izod test system utilizing 1/4 inch test samples is beyond this critical thickness and such tests show a relatively low impact strength with brittle failure mode.
A blending of two polymers generally results in an admixture, assuming good compatibility of the blend components, which is characterized by properties somewhere between the properties of the individual blend components. The value of the specific property under investigation is generally dependent upon the percent of each component in the blend. It has now been found that when certain aromatic polycarbonates are blended in intimate admixture with certain aromatic copolyestercarbonates over a specific percentage ester range, the impact resistance of the composition is higher than either of the individual components as measured by the 1/4 inch notched Izod test. Additionally, the failure mode tends to be more ductile than brittle over a relatively narrow range.